Late last year, a British hen named Gertie stopped laying eggs. She then started crowing like a rooster, and suddenly her entire appearance seemed to morph into a male. So just what is going on here?

Gertie is one of two hens kept by Jim and Jeanette Howard from Cambridgeshire in England. According to Mrs. Howard, both hens produced fewer than average eggs over last winter. Gertie then stopped laying eggs completely, and things got seriously strange when she started moulting her feathers.

Mrs. Howard explains her suddenly robust physique:

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"I thought Gertie came out of that really well. She grew back lots more feathers - she was quite straggly before - and I also realised that she had filled out quite a lot. Gertie looked very healthy."

It seems though that she wasn't simply filling out at last - instead, she was actually taking on a more masculine physique. Soon after, she developed the neck wattle of a rooster, and her comb became much larger. Her behavior changed too, as she started marching around the coop precisely as one might expect a rooster to. Mrs. Howard explains:

"Then a few days later I heard her try to crow. She wasn't very good at it at first, but she's progressed nicely and now she really goes for it. I'm not really sure whether Gertie has actually changed sex, but to all intents and purposes she's now a cockerel."

Veterinarian Marion Ford thinks she knows what happened here. Something in Gertie's feed - most likely a form of fungus - acted as a synthetic hormone for Gertie, causing her to suddenly develop male characteristics. This sort of thing isn't unheard of, but it's only about a 1 in 10,000 chance. Ford explains:

"An increase in testosterone will result in a hen growing an extended comb, exaggerated wattles, and cockerel-like behaviour including strutting and crowing."

That said, even that may not explain everything. As Patrick Morgan explains in Discoblog, Gertie's transformation doesn't quite fit with the latest research on chicken hormones:

These changes may be only outward, or phenotypical, with Gertie remaining a genetically female chicken. The fact that hormones might be the cause of Gertie's outward sex change is especially weird in light of recent research that shows that a chicken's cells are either inherently male or female, regardless of the hormones involved. So how did hormones interact with Gertie's "inherently female" cells to make her look and act like a male? We're not sure.